y=3sin(x/2-π/4)
增区间：
x/2-π/4∈[2kπ-π/2.2kπ+π/2]
x∈[4kπ-π/2,4kπ+3π/2]
所以单调增区间为 [4kπ-π/2,4kπ+3π/2]k∈z
x∈[5π/6,17π/6]
x/2-π/4∈[π/6,7π/6]
所以 y的值域为 [-3/2,3]